1. Field of the Invention
The present invention relates to a plasma processing apparatus used suitably for the etching, ashing and CVD processes in manufacturing large scale integration (LSI) circuits and liquid crystal display (LCD) panels.
2. Description of the Related Art
Plasma generated by the radio frequency (RF) wave or microwave is used widely in the manufacturing process of LSI and LCD devices. Particularly, dry etching based on plasma is indispensable for the manufacturing process of LSI and LCD devices.
RF plasma has been used more often than microwave plasma because of the difficulty of the generation of uniform microwave plasma over a large area in exchange for its advantage of obtaining low-temperature and high-density plasma. The uniformity of plasma is an influential factor for the uniform etching, ashing and CVD processes.
As a plasma processing apparatus capable of producing uniform microwave plasma over a large area, the applicant of the present invention has proposed a plasma processing apparatus having a dielectric sheet, as disclosed in Japanese Patent Application Laid-Open No. 62-5600 and No. 6299481.
FIG. 1A is a schematic plan view of this plasma processing apparatus having a dielectric sheet, and FIG. 1B shows the longitudinal cross section along the line A--A of FIG. 1A. In this plasma processing apparatus, the microwave generated by a microwave generator 24 is directed by a waveguide 23 into a dielectric sheet 21. The microwave propagated in the dielectric sheet 21 forms an electric field in a space 20 beneath it. This electric field penetrates a microwave window 4 and enters a reaction chamber 1 through a microwave lead-in opening 3. The electric field excites gas in the reaction chamber 1, and plasma is generated. By the generated plasma, the surface of a sample S is processed.
The dielectric sheet 21 is made of fluorcarbon polymer such as Teflon (registered trademark). The microwave window 4 is made of a material having a high thermal durability, microwave transmissibility and small dielectric loss, e.g., quartz or ceramics (SiN, A1.sub.2 O.sub.3, etc.).
The dielectric sheet 21 consists of an entry section 211, a fan-out section 212 and a flat section 213. The microwave led by the waveguide 23 enters the dielectric sheet 21 at the entry section 211, expands in the transverse direction in the fan-out section 212, and proceeds to the flat section 213. Based on this structure, the microwave can be propagated with a uniform transverse distribution in the large flat section 213.
With this dielectric sheet provided, the plasma processing apparatus can readily generate plasma over a large area by having a large flat section 213 of the dielectric sheet 21, a large microwave window 4 and a large microwave lead-in opening 3. Plasma processing apparatus, including the one with the dielectric sheet mentioned above, which generate large and uniform plasma beneath a large microwave window have a superior ability of plasma processing based on the resulting high-density and highly active plasma near the microwave window.
In recent years, large glass substrates are used for liquid crystal display panels, and there are intense demands for apparatus that are capable of uniformly processing glass substrates of 400-by-400 mm or larger. Plasma processing apparatus mentioned above attain the uniformity of plasma by using large microwave windows, and the apparatus need to have much larger microwave windows to meet the sizes of substrates to be processed.
However, plasma is generated in the reaction chamber under reduced pressure, and therefore the microwave window must be durable against the differential pressure between the interior and exterior of the reaction chamber. A larger microwave window needs to be thicker.
A thicker microwave window has a greater difference of temperature between the inner side of the reaction chamber which is heated by plasma and the outer side, and there arises the problem of the breakage of window due to the thermal strain. Moreover, a thicker microwave window is heavier and therefore difficult to handle. Microwave windows made of quartz or alumina are expensive, and therefore a microwave window having an increased thickness will be more costly.
It is difficult to manufacture uniformly a large sheet of quartz or alumina used for the microwave window, and therefore a too large microwave window is subjected to uneven dielectric heating and is more prone to break due to the thermal strain.